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Composite photo taken on June 15, 2017 shows a quantum communication ground station in Urumqi, capital of northwest China's Xinjiang Uygur Autonomous Region. Chinese scientists on Thursday reported a major breakthrough in quantum communication: A pair of entangled photons over a distance of 1,200 km have been successfully transmitted from space to Earth. The previous record was about 100 km. (Xinhua/Jin Liwang)

The precision that Chinese scientists have achieved in their latest quantum experiment is just like catching with a piggy bank a chain of coins dropped out of a plane 10,000 meters above. The result is an outstanding landmark in the human history of communication and physical science, and reaches far and more.

On Thursday, Chinese researchers accomplished a successful distribution of "entangled" photon pairs from space to the Earth. After the pairs being sent from the orbiting Micius quantum satellite at distances varying from 500 km to 2,000 km down to two ground locations 1,203 km apart in China, the photon entanglement is still there.

Such a success in demonstrating what Albert Einstein calls "a spooky action at a distance" is not merely a world record, a milestone achievement in global quantum research, but also of technological significance to potential application and fundamental research as a cover story of the prestigious journal Science lauds.

It "lays a reliable technological foundation for large-scale quantum networking and quantum communication experimental research, as well as experimental testing of basic principles of physics such as general theory of relativity and quantum gravity in outer space in the future," said Pan Jianwei, chief scientist for the Micius satellite project and the study's leading author.

In an unprecedented try with high precision, the Chinese research team led by Pan, professor at the University of Science and Technology of China, made Micius a photon pairs' distributor with satellite-to-ground downlinks.

By the Micius-enabled approach, Chinese researchers for the first time in the world demonstrated quantum entanglement over more than 1,000 km.

This figure shows a huge leap over two decades -- up from a span of 144 km in 2007, and several hundreds meters in 1998 in experiments outside a lab.

The work impresses Seth Lloyd, director of the Center for Extreme Quantum Information Theory at the Massachusetts Institute of Technology, as "a true breakthrough in the technology of entanglement distribution."

"The experiment shows that long-range quantum communication is indeed technologically feasible and holds out the promise of the construction of long-rang quantum communication networks in the near future," he further commented.

Thomas Jennewein, an associate professor of quantum information at the University of Waterloo, said this prospect means "improved efficiency, more secure communications."

The latter refers to entanglement-based quantum key distribution, which is so far the only way to establish secure keys between two distant locations on Earth without relying on trustful relay.

Regarding quantum networking or internet, Jennewein described Thursday's quantum experiment result as "a very important milestone, because disseminating quantum entanglement is a first (and most important) building block."

More things to be done including improving quantum entanglement sources to have a much larger emission rate, and photon detectors, he said.

The scientist added that it is needed to conduct "more research on ground-based systems such as quantum memories, quantum processors."

"Going forward, it is not very difficult to speculate that we will see the distribution of quantum entanglement on a global scale one day," said Jennewein.

Alexander Sergienko, a quantum physicist at Boston University, said the latest Chinese quantum experiment result is a "very decisive step" in fundamental research.

"This is another very decisive step in proving the validity of quantum mechanics...over such a global scale. It is hard to overestimate the impact of this result on the development of modern quantum physics," he said.

On top of entangled quantum distribution, Micius-based experiments underway include satellite-to-ground quantum key distribution, and quantum teleportation, among others, and "more results of experiments are expected to be published within this year," said Peng, Micius scientific applications chief designer.

Apart from direct use in secure communications, entangled quantum distribution can also serve the efforts to realize quantum teleportation, Peng stressed.

He said that among what Chinese researchers plan to do next is to expand satellite coverage so as to accomplish round-the-clock quantum communications. (Xinhua)

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(Editor: CHEN Na)

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